DE4138309C2 - By the action of electromagnetic radiation crosslinkable plastic material - Google Patents

Description

The invention relates to an electromagnetic effect Radiation crosslinkable or curable plastic material for producing a three-dimensional object by means of Stereographie as well as the production of this plastic material.

Under the name "stereography" or "stereo lithography "known method becomes a three-dimensional Object layer by application and subsequent Solidifying successive layers of an initially made of liquid material. The consolidation takes place there at preferably by a bundled light beam in the form a laser or the like, corresponding to the object corresponding to the object Make the layer is directed and there the solidification causes the material. The material must therefore by Lichtein effect or generally by the action of electromagnetic Radiation be solidified.

Usually, the material will be at normal conditions liquid, monomeric or oligomeric plastic used, its solidification when exposed to light by polymerization he follows. Such mixtures are commercially available. Other materials are described in EP 03 78 144 A2.  

From DE 29 17 483 A1 is a photosensitive recording material known for use in printing, the both a difunctional monomer, a functional one aliphatic urethane as well as a photoinitiator. Furthermore, from DE 26 11 577 A1 such a recording material with a carbonate known as monomer.

It is an object of the present invention to provide a plastic material of the above type to create that the requirement ments that the stereography method attaches to such a mate rial provides, met at reasonable cost. In particular sol len favorable properties for mechanical Weiterver processing of the models can be achieved after curing.

The following requirements apply to the material:

• 1. the viscosity must be within a certain range; if it is too high, the liquid layer can not be fast and applied evenly enough; is she too low, is the volume change during solidification and thus the deformation of the object too large; As a general rule the viscosity should be below 6 Pa · s;
• 2. The deformation of the object due to the density change in the polymerization must be as low as possible; the Shrinkage of the plastic material in the Polymerisa tion should be below about 6%;
• 3. The sensitivity to radiation should be possible be as high as possible, so that the fastest possible weitge Hende polymerization at relatively low radiation energy - and thus a high operating speed - is reached and also the risk of further deformations conditions before and at the usually required post-curing of the object by UV irradiation as low as possible is;
• 4. Good mechanical properties after polymerization (high breaking and elongation at break, low impact sensitivity or brittleness, elastic properties), so that Also a machining is possible.

The solution of the stated object consists according to the invention in a plastic material having the Be mentioned in claim 1  stood share.

This results in the properties of the polymerized Ma terials from the properties of the polymerized stock parts. The polycarbonate combines the good qualities of Light metal, glass and plastic such as low impact sensitivity, Translucence, flexural strength, dimensions stability and temperature resistance. The polyurethane causes good flexibility, responsiveness, hardness, adhesion property and chemical stability.

Preferably, a carbonate of the formula (I)

and an oligomeric urethane of the formula (II)

used, wherein R, R ₁ and R ₂ each represent alkyl groups. For example, for R ₁ and R ₂ each is a group having the formula

where R is an alkoyl radical or hydrogen atom represents.

A carbonate with the formula (I) owns a lot low viscosity of 0.2 Pa · s at 25 ° C. An aliphatic one Urethane having the formula (II) is at 25 ° C pasty.

So that the viscosity is within the desired range, the Mass fraction of the carbonate amount to at least 50%; in this  Case, the viscosity is below 6 Pa · s at temperatures of 20 ° C and above; Preferably, this proportion is not greater than 70%, otherwise the deformation of the object becomes too large. Particularly preferred is a carbonate content of about 60%.

The mass fraction of urethane is preferably between 20% and 50%, more preferably about 40%; this results compared to the commercial material a much reduced E modulus or Young modulus and thus a greatly improved Breakage or elongation at break.

As photoinitiator, all substances are suitable, which are under Ein flow of the radiation used for the polymerization free Radi form kale. Preferably, an acetophenone, be particularly Preferably dimethoxyphenylacetophenone (DMPA) is used. at Use of a helium-cadmium laser is preferably one Initiator that uses a mixture of the same Mas sen proportions of 1-hydroxy-cyclohexyl phenyl ketone and Benzophenone represents. When using an argon laser is preferably 2,2-dimethoxy-1,2-diphenylethane-1-one or 2-2-dimethoxy-2-phenylacetophenone used.

It was found that the optimal concentration of the Photoinitiators, d. H. the concentration in which as possible short exposure time as far as possible Polymerization or the highest possible product strength and Penetration of the polymerization is achieved by Wel wavelength of the radiation source depends. The preferred concentrate tion range was generally 1 to 5% by mass DMPA or the photoinitiator determined. Within the meaning of the invention was optimal for an argon laser as a radiation source a Concentration of 1.5 to 2.5 mass%, more preferred about 2% by mass, and for a helium-cadmium laser as Radiation source a concentration of 2.5 to 3.5 mass%,  most preferably about 3 mass% determined. Depending on ge desired polymerization depth can be a little higher or lower value.

To influence the properties of the finished object kön According to the invention, two further substances are added. These are on the one hand acrylates, for example, diacrylate 101, and silane compounds of the formula (IV)

SiR₁R₂R₃R₄ or Si₂R₁R₂R₃R₄R₅R₆ (IV)

for example, ebceryl,
wherein the groups denoted by R ₁ to R ₆ each may represent hydrogen atoms (H), chlorine atoms (Cl), hydroxy groups (OH) or vinyl groups (-CH = CH ₂ ). A suitable diacrylate is, for example, a di-ethoxylated bisphenol A dimethacrylate of the formula

The acrylates cause an improvement of the optical properties and aging resistance. In particular lead However, they also to a greater hardness and lower fracture or Elongation at break of the object. For example, a Mas 10% of a diacrylate called Bisphenol A to a reduced to half the elongation at break. An addition of the acrylate is so low, if a grö ßere hardness and brittleness to be achieved.  

The silane compounds constitute a large group of chemi compounds whose molecules are represented by silicon atoms are formed on which alternately with oxygen atoms Carbon radicals are implanted. These fluids have a very low surface tension (about 20 dynes / cm), those for their antifoaming and wetting properties responsible. These properties can fiction be used advantageously according to.

Namely, a layer of liquid plastic thereby worn that the object in a bath from the liquid Plastic is lowered, then there is a risk of one conclusion of bubbles. Already an addition of 1 to 3 Mass% of a silane compound of the formula (IV) to the Liquid plastic can cause this hazard due to it significantly reduce reduced surface tension. Further The liquid plastic material flows more easily over the lowered surface, so that the working speed increases becomes.

For the mass fractions of the above-mentioned substances, the following became determined favorable areas:

Carbonate: at least 50%
Urethane: between 20% and 50%;
Diacrylate: between 0% and 30%
Silane: between 0% and 3%.

Particularly preferred is a plastic material consisting of 60 parts carbonate, 40 parts urethane, 1 to 3 parts ebceryl depending on working temperature and either 2 parts DMPA (photoinitiator) using a Argon lasers or 3 parts DMPA using a Helium-cadmium laser. Such a plastic material be sits mechanical properties, which in their sum for the Further processing of the object after laser hardening are optimized.  

All products are under the indicated designations available on the market. Other stabilizers than those that are already in these products (eg Hydroquinone), are not required.

The plastic compound according to the invention is produced, by first adding the urethane (formula II) to a maximum of 60 ° C, before Preferably at about 50 ° C, is heated and then the carbonate (Formula I) is added with simultaneous stirring. to If necessary, the additives, acrylate and / or silicone, and finally the photoinitiator given. If you put the o.a. particularly preferred material this way, the following properties result:

Density of the monomer / polymer: 1.23 / 1.30 kg / dm³ Volumetric shrinkage: 6% Viscosity: 5 Pa · s Young's module after complete polymerization: 450-900 Elongation at break after complete polymerization: 20%

A stereography method in which the described art fabric material to be used according to the invention is for example in Kodama, Rev. Sci. Instr. 52 (11), pages 1170-1173 (1981).

Claims (13)

1. Plastic material crosslinkable by the action of electromagnetic radiation for producing a three-dimensional object by means of stereography, comprising:

• a) at least 50% by mass of a monomeric or oligomeric difunctional carbonate;
• b) a monomeric or oligomeric mono-, di- or polyfunctional aliphatic urethane; and
• c) a photoinitiator.

2. Plastic material according to claim 1, characterized by a carbonate according to the formula and a urethane according to the formula wherein R, R ₁ and R _{2 are} each alkyl groups. 3. Plastic material according to claim 1 or 2, characterized in that as a photoinitiator Dimethoxyphenylacetophenone (DMPA) is used. 4. Plastic material according to one of claims 1 to 3, characterized characterized in that it comprises a photoinitiator with a mass fraction of between 1% and 5%. 5. Plastic material according to claim 4, characterized in that the mass fraction of the  Carbonates between 50% and 70% and the mass fraction of Urethane is between 30% and 50%. 6. Plastic material according to claim 5, characterized by 60 mass% carbonate and 40% by mass of urethane. 7. Plastic material according to one of claims 4 to 6, characterized in that the mass fraction of the Photoinitiators between 2% and 3%. 8. Plastic material according to one of claims 1 to 7, characterized by an addition of a maximum of 50% by mass of acrylate and / or an addition of a maximum of 3% by mass of a silane compound of the formula SiR₁R₂R₃R₄oderSi₂R₁R₂R₃R₄R₅R₆Wobei the R ₁ . , , R _{6 are formed} from hydrogen atoms (H), chlorine atoms (Cl), hydroxy groups (OH) or vinyl groups (-CH = CH ₂ ). 9. Plastic material according to claim 8, characterized by the following composition:
60 parts by mass carbonate;
40 parts by mass of urethane;
1-3 parts by mass of the silane compound; and
2 to 3 parts by mass of photoinitiator. 10. Production of a plastic material according to one of the An Proverbs 1 to 9, characterized in that the selected amount Urethane heated to 40-60 ° C, preferably 50 ° C and there after stirring, add the selected amount of carbonate and finally the photoinitiator is added. 11. Method for producing a three-dimensional ob by means of stereography, where the object is in a bath of liquid art fabric material in layers by exposure Electromagnetic radiation is crosslinked, characterized in that a plastic material after one of claims 1 to 9 is used. 12. The method according to claim 11, characterized in that the plastic material is about Contains 2% by mass of the photoinitiator and the Crosslinking by irradiation of a layer of art fabric material is carried out with an argon laser. 13. The method according to claim 11, characterized in that the plastic material is about Contains 3 mass% of the photoinitiator and the Crosslinking by irradiation of a layer of art fabric material durchge with a helium-cadmium laser leads.